The use of vapor storage devices, particularly in vehicles, to control fuel evaporation has been utilized previously. A typical fuel vapor storage device consists of a container holding a quantity of activated charcoal or the like which is the preferred medium for storing fuel vapors. Because the storage capacity of a given quantity of charcoal is limited, it is necessary to periodically purge the vapor storage device with fresh air to remove fuel vapor and pass it to an operating engine for subsequent treatment by other control devices, such as a catalytic converter. Normally, this purging occurs when the engine is operating at a moderate load and speed.
Typical vapor storage devices are disclosed in U.S. Pat. Nos. 4,134,378; 4,137,882 and 4,280,466. These devices share a common construction in that they utilize a generally cylindrical enclosure which is at least partially filled with a vapor storage medium such as activated charcoal. However, these patents disclose a charge of activated charcoal in a generally cylindrical configuration. An inlet for fuel vapor and an inlet for purging air is located centrally of the cylindrically shaped activated charcoal. Both when the fuel vapor enters the storage device and when air is drawn through the charcoal, the flow path of the vapor or air takes the form of a truncated cone through the activated charcoal with the small meeting in the vicinity of the central inlet. Thus, any activated charcoal outside the boundaries of this cone are rendered relatively ineffective both for storage of fuel vapor or for purging. It has been found that standard canisters of this aforedescribed description are generally only effectively purged by about 30 percent and, thus, their storage efficiency is quite low. The subject improved vapor storage device is believed to be effectively purged by as much as 90 percent of storage volume and, thus, the quantity of needed charcoal for storing fuel vapor is less, or conversely, much more is effectively utilized.